Monday, February 1, 2010

F70EXR Strange Flash Behavior

I received a comment this morning that suggested that the flash on the F70EXR was pretty wonky in daylight and indoors. The standard indoor complaint of 800ISO being too high is understandable, but that’s just how it works when the flash is so weak. But the upside is nice backgrounds, so I consider that a small price to pay.

But what about outdoor shots in sunlight? What is going on there?

I ran a quick experiment and came to some startling conclusions. The cam does not appear to be binning once you turn on the flash … and that forces higher ISO if you leave it at DR400 as I do … and *that* forces F11, which causes the subject to be severely underexposed …

In other words, you might as well not shoot flash at all if you don;t set ISO 100 manually … outdoors, remember.

These were shot indoors facing out. The subject is backlit only, which means that the only light on it comes from the flash. Both are P mode M size and DR400. The only difference is that the first image was shot auto ISO 1600 and the second ISO 100.

DSCF3432 f/11   1/200    ISO400    DR400


DSCF3433f/5.6   1/125   ISO100    DR100 

So … the exposures are quite different … let’s calculate the total difference second image minus first image:

  • Aperture: +2 stops
  • Shutter: +.75 stops
  • ISO: –2 stops
  • DR: somewhat brighter

The aperture and ISO cancel out. The shutter shows an increas of 3/4 stops in exposure, and the dynamic range dropping to 100% means that the highlights will be somewhat brighter. The next effect is about 1 stop brighter, and there is no question that the background of the bottom shot is brighter.

*But* … the flash should compensate and light the subject correctly either way, and the subject is far too dark above. Why? Perhaps the computational algorithms in camera are incapable of handling the choice of f.11 … or the flash is really that weak.

But the flash *cannot* be too weak. The aperture and ISO difference is netted out. So the *same* power out of the flash will result in the same exposure on the subject.

Yet the subject is dark. This tells me that the cam is confused. My guess is that the hack they use to boost aperture to keep the shutter speeds within range was not properly hooked to flash mode. In fact, they seem to use the *software* ISO/DR algorithms even in M mode as soon as the flash goes on. Yet I would bet that this was unnecessary … just a feature interaction in that mess of firmware of which they have clearly lost control …

Again … that software team should be fired … or the boss … whatever. Fuji need an enema and the software team is where I would stick it …

Anyway … I don;t think there is any reason why the software ISO/DR hookup that they use for large images should be necessary in M mode. The flash’s confusion if probably brought about by hacks in one area of the firmware that were not ported to all areas. And a lack of thorough testing. (Come on guys … no backlight tests? Really?)

So … score one for the bad guys … someone on that team dropped the ball.

The fix … it sucks, but you have to set DR100 and auto ISO or ISO 100, which will set DR100 for you. Whatever you do, you will get “too bright” highlights, which is *not* what you want on a sunny day where your subject is backlit.


1 comment:

Jason Davis said...

Ah ha! I was wondering why my photos taken outdoors with fill flash always appeared to be darker than expected. Oh well, I still have my f31fd, it works fine outdoors with fill flash :)